Drug delivery has been a persistent challenge in the pharmaceutical arts, particularly when a drug is unstable and/or poorly absorbed at the locus in the body to which it is administered. One such class of drugs includes 2,5-diketopiperazines, which is represented by the compound of the general Formula 1 as shown below where E=N.
These 2,5 diketopiperazines have been shown to be useful in drug delivery, particularly those bearing acidic R groups (see for example U.S. Pat. Nos. 5,352,461 entitled “Self Assembling Diketopiperazine Drug Delivery System;” 5,503,852 entitled “Method For Making Self-Assembling Diketopiperazine Drug Delivery System;” 6,071,497 entitled “Microparticles For Lung Delivery Comprising Diketopiperazine;” and 6,331,318 entitled “Carbon-Substituted Diketopiperazine Delivery System,” each of which is incorporated herein by reference in its entirety for all that it teaches regarding diketopiperazines and diketopiperazine-mediated drug delivery). Diketopiperazines can be formed into particles that incorporate a drug or particles onto which a drug can be adsorbed. The combination of a drug and a diketopiperazine can impart improved drug stability. These particles can be administered by various routes of administration. As dry powders these particles can be delivered by inhalation to specific areas of the respiratory system, depending on particle size. Additionally, the particles can be made small enough for incorporation into an intravenous suspension dosage form. Oral delivery is also possible with the particles incorporated into a suspension, tablets or capsules; or dissolved in an appropriate solvent. Diketopiperazines may also facilitate absorption of an associated drug. Nonetheless difficulties can arise when diketopiperazines are diacids, or are in diacid form(s), due to the limited solubility of these diacids at non-basic pH (i.e., neutral or acid pH). Another difficulty arises because these diacid diketopiperazines may form disadvantageous association(s) with some drugs.
Therefore there is a need for diketopiperazine compositions having greater solubility at a neutral and/or acidic pH and methods for their use in the manufacture of therapeutic compositions.